Who Gave Humanity the Genital Herpes Virus?

Scientists have discovered the ancient hominin species that gave Homo erectus the genital herpes virus.

A cast of a P. boisei skull, used as a teaching aid at Cambridge University [Photo by Louise Walsh]

There are two herpes simplex viruses that affect primates. The viruses manifest in modern humans as cold sores, or HSV1, and genital herpes, or HSV2. Our early human ancestors retained only the genes for HSV1 when their lineage split from chimpanzees, and almost skipped out on the HSV2 virus. Almost. Somewhere down the evolutionary line, about 1.4 to three million years ago, HSV2 was able to transfer from a different species back to our human ancestors.

According to a new study, a hominin species called Parathropus boisei was the bridge that enabled HSV2 to jump from the ape lineage back to the human lineage. P. boisei stood at about four feet tall, with a wide face, a heavyset build, and a relatively small brain. Scientists say that P. boisei likely contracted the virus by scavenging ancestral chimp meat. Fluid exchange though chimp bites or scratches could have also transfered the virus.

Sex, Eating, or Both

A statue of an adult Homo erectus female [Photo by Tim Evanson/Wikimedia Commons]

1.4 to three million years ago, ancient chimps, P. boisei, and Homo erectus were all in Africa, concentrated in an area from which modern humans would eventually evolve. It's therefore extremely likely that the three species came into contact with each other. The genital herpes virus was also evolving at that time as well.

HSV1 may have protected hominins from HSV2, which was also able to infect the mouth. However, according to the researchers, HSV2 "adapted to a different mucosal niche". That niche happened to be in the genitals.

So how could P. boisei have transmitted the virus back to our human ancestors? P. boisei and H. erectus likely had many encounters around sources of water, such as Kenya's Lake Turkana. Members of the two species may have engaged in sexual intercourse with each other, or H. erectus may have hunted P. boisei and consumed them. It may have been both. There's evidence that about two million years ago, H. erectus developed the ability to hunt and butcher.

“Once this virus gains entry to a species it stays, easily transferred from mother to baby, as well as through blood, saliva and sex,” says Dr. Charlotte Houldcroft, one of the researchers.

How the Genital Herpes Virus Boomeranged

Transmission electron micrograph of a herpes simplex virus

The transfer of HSV2 from chimps to humans could have gone as thus: P. boisei may have consumed HSV2-infected chimp meat, and H. erectus may have consumed infected P. boisei meat. H. erectus then passed the virus on to modern humans.

The researchers were able to arrive at their conclusions by studying fossils, herpes DNA, and even ancient African climates. “Climate fluctuations over millennia caused forests and lakes to expand and contract," said Simon Underdown, another of the researchers. "Layering climate data with fossil locations helped us determine the species most likely to come into contact with ancestral chimpanzees in the forests, as well as other hominins at water sources.”

It was in this way that researchers were able to ascertain that P. boisei was the culprit behind bringing the genital herpes virus back into our lineage.